Food waste or organic waste management is a global issue. Currently about 40% of edible food goes into waste from its journey from farm's crops to the dining table. About 30-40% of all the waste humans generate is composed of food waste. If not dealt with properly, it may create problems in terms of infections, pollution and unpleasant smells.
Traditional waste management practices include landfills, composting, incinerator, dehydration, pyrolysis and gasification. Food waste diverted to landfills generates methane (CH4), which is much more potent than carbon dioxide (CO2) as a greenhouse gas. It is believed that the vast amount of food currently going to landfills makes a significant contribution to global warming.
Food waste may lead to an increased and wasteful use of chemicals such as fertilizers and pesticides. Transporting food waste requires use of more fuel and more rotting food generates more methane. All waste management practices require transportation and have other logistics and environmental down sides. Space required for new and larger landfills and/or for large-scale composting of food waste may be difficult to find or not available in some areas. As an alternative, incinerators can be pollution-driven expensive operations.
Recently, various municipalities are making and enforcing new regulations requiring the separate disposal of food/kitchen waste from regular waste.
The following terms are abbreviated herein as follows.
‘Biological Oxygen Demand’ is abbreviated as BOD,
‘Chemical Oxygen Demand’ is abbreviated as COD,
‘Total Suspended Solids’ is abbreviated as TSS, and
‘Fats, Oils and Grease’ is abbreviated as FOG.
According to United Nations Environment Program (UNEP), roughly one third of food produced in the world for human consumption every year, approximately 1.3 billion tonnes, gets lost or wasted.
Commercial food waste disposal systems or food waste digesters resolve many of the above issues. Food waste disposal systems are a relatively promising tool to manage large-scale food waste on-site without the need for further transportation or hauling. Food waste disposal systems convert organic food waste into trade effluent or gray water with help of microbial/enzymes bio-processing within 12-24 hours under controlled environmental conditions. Food waste disposal systems (or food waste digesters) generate trade effluent that is composed of water, fats, oils, fatty acids, proteins, amino acids, lipoproteins, glycoproteins, nucleic acids, a variety of carbohydrates, organic acids, and volatile organic compounds, etc.
Food waste ingredients present in the trade effluent contribute to conventionally higher levels of BOD, COD, TSS, FOG, color and odor.
The most common contaminants present in trade effluent include soluble and insoluble carbon and nitrogen compounds that contribute to BOD.
BOD is a measure of the oxygen required for biological degradation of the contaminants in trade effluent and is generally correlated to the amount of organic material contained in that trade effluent. In other words, the greater the organic matter content of a trade effluent, the higher will be the BOD level of that trade effluent. In order to meet the regulatory trade effluent wastewater discharge standards in most parts of North America and worldwide, the BOD levels must be below 50 mg/L prior to discharge into municipal sewer line. The BOD levels of trade effluent from commercial food waste disposal systems can go as high as 35,000 mg/L. If this trade effluent is discharged into municipal sewer without treatment, it creates extra load for the municipal wastewater treatment plant. Additionally, higher levels of TSS and FOG may cause blockage of sewer pipes and that requires an expensive maintenance.
Currently, there is no reliable technology available that can effectively treat trade effluent generated by the food waste disposal systems or food waste digesters in order to meet global environmental and/or municipal standards.
On-site conversion of organic food waste to water has several economical, logistical and environmental benefits compared to the traditional waste management technologies. Despite all those benefits, the following major reasons act as limiting factors in implementing the organic food waste disposal technology on a large scale. First, an average commercial food waste disposal system/digester with a food waste capacity of 1000 kg per day consumes at least 1000 liters of fresh water per day. Many places in North America and around the world simply can't afford to deliver 1000 liters of fresh water on daily basis to the food waste digester system. Second, the trade effluent produced by most of the commercially available food waste digesters and food waste disposal systems generate relatively higher amounts of BOD, COD, TSS, FOG, color and odor that may not meet municipal regulatory limits. Third, the offensive odor generated by trade effluent is detrimental to the employees working in close proximity. Fourth, there is a general belief, though unscientific and without concrete evidence, among municipal authorities that microorganisms/enzymes discharged along with trade effluent wastewater may harm sewer pipes or the municipal wastewater treatment plant.
There is a need for an effective treatment of trade effluent discharged from food waste disposal systems, preferably that is economical, effective, eco-friendly, reliable, avoids the use of harsh chemical additives, helps meet municipal wastewater discharge standards, and/or could even recycle treated trade effluent wastewater back into the food waste disposal system.